This invention relates to variable resistors and more specifically to an improved construction of the pattern of the resistive member of such resistors so as to prevent occurrence of electrostatic noise.
In order to improve the accuracy of their output resistance, conventional variable resistors often have a construction as exemplified in FIG. 1. Namely, terminal sections 6 and 8, each consisting of a highly conductive film, are formed on an insulating substrate 1 to connect with a ground terminal and an input terminal, respectively, and a resistive member is formed by a plurality of resistive elements 3, 4 and 5, each having a specific resistance different from that of the others and a generally hemi-crescent shape in which the width becomes progressively narrower from one end to the other. The resistive elements 3, 4 and 5 are connected subsequentially between the abovementioned terminal sections 6 and 8, thus forming a resistive member 2. Typically, the resistive elements are formed by printing carbon paste or the like on the substrate A. The variable resistors of this type further include a slide member 9 having a plurality of contact elements 10 that are brought into sliding contact with the resistive member 2 and are connected to a terminal section 7 communicating with an output terminal.
In the variable resistors of the above-described type, when the contact elements 10 are located at the position of the narrow width of the resistive member 2 as illustrated in FIG. 1, the outer contact elements come off the resistive member 2 and come into direct contact with the surface of the insulating substrate 1 at a location adjacent the resistive element 2. If the slide member 9 is further rotated under this state, static electricity tends to build upon the substrate 1 due to sliding friction between the outer contact elements 10 and the insulating substrate 1 and to other factors and this results eventually in electrostatic noise during operation of the resistor.